nifxml 0.9.1

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Moved nifxml.py and nifxml_doc.py from nifdocsys to nifxml repo. gen_niflib will be moved to niflib so that nifdocsys can be deleted.

Many Oblivion-era fixes, other Havok fixes, and a couple of Niflib fixes.

• 10.0.1.2 was not supported because the condition was assuming a User Version of >=3 for all Bethesda NIFs with BSStreamHeader (User Version 2 + Export Info). However User Version was not actually introduced until 10.0.1.8.
• 10.0.1.0 and 10.0.1.2 are now much more correct in regards to Havok. Especially bhkRigidBody data alignment.
• FO4 is now given correct bhkRigidBody alignment, even though bhkRigidBody is not technically valid for FO4. However, it does occur in NIFs right out of the official exporter and pre-Elric (their NIF post-processor). There was also some demand for editing the values before converting with Elric, or being able to create collisions without 3ds Max and then use Elric.
• Added missing bhkConvexSweepShape type.
• Removed the use of derived type conditions from the compounds for BSPackedCombinedGeomDataExtra as it cannot be assumed that a parser has access to the NiObject including it when parsing the condition.
• NiBlendInterpolator decoding.

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@neomonkeus There is no more that I can fit into 0.9.1 at this point. The rest of the stuff I have in the pipeline is all for 0.9.5 or higher. Just need to know if you have any input on the Python files mostly.

Right now, nifxml.py is really only good enough for the documentation generator in nifdoc.py but I will be fixing up nifxml.py in later versions to have better faculties for XML validation and various analysis. For example I've started adding some Expression validation already.